Method for preparing nano noble metal by directly introducing reducing agent borane cluster into carbon carrier

Abstract

According to the method for preparing the nano noble metal by directly introducing the reducing agent borane cluster into the carbon carrier, the borane cluster weak reducing agent is loaded on the carbon carrier to prepare the loaded nano noble metal through in-situ reduction, and agglomeration of metal sites can be avoided through the weak reducibility of the borane cluster; the reducing agent is introduced to the carbon carrier, and the hard supporting effect of the carbon carrier can also avoid large-scale aggregation of formed metal. The nano precious metal is dispersed in the carbon carrier, the dispersity of the nano precious metal is good, and the size of the nano precious metal is smaller than 10 nanometers. Compared with the prior art, the reducing agent borane cluster is directly introduced to the surface of the carbon carrier, in-situ reduction of precious metal ions is achieved, the high-dispersion small-particle-size supported nanometer precious metal is effectively obtained, and the method is easy to operate, reliable in preparation process, good in repeatability and beneficial to large-scale preparation.

Description

Technical Field

[0001] The present invention relates to a method for preparing a novel nano-precious metal material, belonging to the field of new material preparation, and specifically to a method for directly introducing a reducing agent borane cluster into a carbon carrier to prepare nano-precious metals. Background Art

[0002] At present, approximately 80% of industrial catalytic activities require the participation of catalysts, and the catalytic performance of catalysts is crucial for the efficiency of production lines. Traditionally, large particles of metals are used as catalysts, which is not conducive to improving the atomic utilization rate and mass activity (activity per unit mass) of catalysts. In the past decade, researchers have continuously developed advanced nano-material preparation technologies to minimize the particle size of metal catalysts and increase the participation of surface atoms of catalysts. Currently, the mainstream methods for directly preparing nano-metals by wet reduction using sodium borohydride as a reducing agent, high-temperature reduction in a hydrogen atmosphere to prepare nano-metals, hydrothermal / solvothermal preparation of nano-metals in a closed space, and high-temperature heat treatment of metal-organic framework materials to prepare nano-metals have received extensive participation from researchers. Even so, most of the metal catalysts or metal catalyst preparation methods developed in the academic community at present have not been extended to industrial applications. The main reasons include: (1) directly preparing nano-metals using a strong reducing agent sodium borohydride, the strong reducibility easily causes metal aggregation, and the obtained nano-metal particles have a relatively large particle size; (2) delaying the reduction process to the high-temperature heat treatment stage is likely to cause aggregation of metal sites due to thermal motion during the formation at high temperatures; (3) preparing nano-metals by heat treating metal-organic framework materials is restricted by the high price of metal-organic framework materials. Generally, maintaining the metal size on the surface of metal-based catalysts below 10 nanometers can adapt to most industrial catalytic processes and also maintain a high activity per unit mass. Therefore, continuing to develop new technologies for preparing novel nano-metal materials is crucial for promoting the development of nano-metal catalysts and their industrial applications. Summary of the Invention

[0003] The technical problem solved by the present invention is to provide a method for in-situ constructing a highly dispersed nano-precious metal material by modifying a weak reducing agent onto a carbon carrier. The nano-metals prepared by the method provided by the present invention have a high dispersion degree and a size below 10 nanometers.

[0004] The specific technical solution adopted by the present invention is as follows:

[0005] A method for directly introducing a reducing agent borane cluster into a carbon carrier to prepare nano-precious metals, comprising the following steps:

[0006] A. Introducing a borane cluster weak reducing agent onto a carbon support: Dissolve a borane cluster with an organic cation in an organic solvent solution, then add a carbon support dispersed in the organic solvent, and then continuously stir and add a poor solvent, water. The purpose is to precipitate the borane cluster from the surface of the carbon support and in-situ load it on the carbon support. Collect the solid by filtration and dry it to achieve introducing the borane cluster weak reducing agent onto the carbon support;

[0007] B. Reducing metal ions on the carbon support containing borane clusters to prepare nano-metals: Redisperse the carbon support loaded with borane clusters obtained in step A in water, add an aqueous solution of a noble metal salt under reflux at 120 °C, and continuously stir to convert the noble metal ions into nano-metals on the carbon support. Filter and separate the solid and dry the solid to achieve reducing metal ions on the carbon support to prepare nano-metals;

[0008] In step A, the anionic part of the borane cluster can be dodecahydrododecaborate anion, decahydrodecaborate anion, hexahydrohexaborate anion, and the cation of the borane cluster can be tetrabutylammonium cation, protonated triethylammonium cation, tetraethylammonium cation.

[0009] In step A, the carbon support can be carbon nanotubes, nitrogen-doped carbon nanotubes, nitrogen-doped hollow carbon tubes, graphene, graphene oxide, hollow carbon spheres, nitrogen-doped hollow carbon spheres.

[0010] In step A, the organic solvent can be methanol, ethanol, acetonitrile, ethyl acetate, dichloromethane, chloroform.

[0011] Specific implementation of step A: Weigh 313.0 mg (0.5 mmol) of TBA2(B12H12) (TBA is tetrabutylammonium cation, B12H12 is dodecahydrododecaborate anion) and dissolve it in 50 mL of methanol, then add a nitrogen-doped hollow carbon tube support dissolved in 50 mL of methanol. Subsequently, add 500 mL of ultrapure water dropwise to the above mixture under stirring, separate the solid by suction filtration, and wash the filter cake with ultrapure water three times to obtain a nitrogen-doped hollow carbon tube coated with a borane cluster reducing agent on its surface.

[0012] In step B, the noble metal salt can be chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, ruthenium trichloride, sodium chloropalladate, chloroauric acid, iridium trichloride.

[0013] In step B, the duration of continuous stirring can be 0.5 - 6 hours.

[0014] The specific implementation of step B is as follows: The nitrogen-doped hollow carbon tubes with borane clusters on the surface are redispersed in 200 mL of ultrapure water (the container is a 500 mL round-bottom flask), and the round-bottom flask is transferred to an oil bath at 120 °C. Under reflux conditions, 20 mL of potassium hexachloroplatinate solution (with a molar amount of 0.05 mol) is injected into the mixed dispersion. After reacting for 2 hours, the reaction solution is cooled to room temperature, and then the filter cake is collected by filtration. The filter cake is washed 3 times with ultrapure water and methanol respectively, and then dried in a blast dryer at 60 °C for 12 hours to obtain nitrogen-doped hollow carbon tubes loaded with nano-platinum.

[0015] The present invention provides a method for directly introducing a reducing agent borane cluster into a carbon carrier to prepare nano-precious metals, which is obtained according to the above preparation method. Loading the weak reducing agent borane cluster on the carbon carrier to in-situ reduce and prepare the supported nano-metal can avoid the aggregation of metal sites by using the weak reducibility of the borane cluster; introducing the reducing agent onto the carbon carrier, the hard support effect of the carbon carrier can also prevent the formed metal from aggregating on a large scale. The nano-precious metals are dispersed in the carbon carrier, and the dispersion of the nano-precious metals is good, and the size is less than 10 nanometers. In the present invention, by directly introducing the reducing agent borane cluster onto the surface of the carbon carrier, in-situ reduction of precious metal ions is realized, and highly dispersed and small-particle-size supported nano-precious metals are effectively obtained. This method has simple operation, reliable preparation process and good repeatability, which is conducive to large-scale preparation. Description of the Drawings

[0016] Figure 1 It is the aberration-corrected transmission electron microscope image of nitrogen-doped hollow carbon tubes loaded with Pt;

[0017] Figure 2 It is the aberration-corrected transmission electron microscope image of nitrogen-doped hollow carbon tubes loaded with Ru;

[0018] Figure 3 It is the aberration-corrected transmission electron microscope image of nitrogen-doped hollow carbon tubes loaded with PtRu;

[0019] Figure 4 It is the powder X-ray diffraction signal of mesoporous carbon spheres loaded with nano-platinum. Detailed Description of the Invention

[0020] The following presents the specific operations of the present invention in combination with examples.

[0021]

Example 1

[0022] A method for directly introducing a reducing agent borane cluster into a carbon carrier to prepare nano-precious metals, comprising the following steps:

[0023] Weigh 313.0 mg (0.5 mmol) of TBA2(B12H12) (TBA is tetrabutylammonium cation, and B12H12 is dodecahydrododecaborane cluster anion), dissolve it in 50 mL of methanol, and then add the nitrogen-doped hollow carbon tube support dissolved in 50 mL of methanol. Subsequently, 500 mL of ultrapure water was added dropwise to the above mixture under stirring conditions. The solid was separated by suction filtration, and the filter cake was washed 3 times with ultrapure water to obtain the nitrogen-doped hollow carbon tube coated with borane cluster reducing agent on the surface. The nitrogen-doped hollow carbon tube coated with borane cluster on the surface was dispersed again in 200 mL of ultrapure water (the container is a 500 mL round-bottom flask), and the round-bottom flask was transferred to an oil bath at 120 °C. Under reflux conditions, 20 mL of potassium hexachloroplatinate solution (the amount of substance is 0.1 mol) was injected into the mixed dispersion; after reacting for 2 hours, the reaction solution was cooled to room temperature, and then the filter cake was collected by filtration. After the filter cake was washed 3 times with ultrapure water and methanol respectively, it was dried in a blast dryer at 60 °C for 12 hours to obtain the nitrogen-doped hollow carbon tube loaded with nano-Pt.

[0024] Characterization results of the product obtained in Example 1:

[0025] Figure 1 It is the aberration-corrected transmission electron microscope image of the nitrogen-doped hollow carbon tube loaded with Pt obtained in Example 1. This result shows that nano-metals have been uniformly loaded on the hollow carbon tube. In the high-angle annular dark-field imaging mode, the high-contrast white bright spots are metal sites, and the metal site in Example 1 is nano-Pt. This result indicates that by loading the borane cluster weak reducing agent on the carbon support to in-situ reduce and prepare the supported nano-Pt, the weak reducibility of the borane cluster can be used to avoid the agglomeration of Pt; when the reducing agent is introduced onto the carbon support, the hard support effect of the carbon support can also prevent the formed nano-Pt from aggregating on a large scale.

[0026]

Example 2

[0027] Weigh 313.0 mg (0.5 mmol) of TBA2(B12H12) (TBA is tetrabutylammonium cation, and B12H12 is dodecahydrododecaborane cluster anion), dissolve it in 50 mL of methanol, and then add the nitrogen-doped hollow carbon tube support dissolved in 50 mL of methanol. Subsequently, 500 mL of ultrapure water is added dropwise to the above mixture under stirring conditions. The solid is separated by suction filtration, and the filter cake is washed 3 times with ultrapure water to obtain the nitrogen-doped hollow carbon tube with borane cluster reductant coated on its surface. The nitrogen-doped hollow carbon tube with borane cluster coated on its surface is dispersed again in 200 mL of ultrapure water (the container is a 500 mL round-bottom flask), and the round-bottom flask is transferred to an oil bath at 120 °C. Under reflux conditions, 20 mL of ruthenium trichloride solution (the amount of substance is 0.1 mol) is injected into the mixed dispersion; after reacting for 2 hours, the reaction solution is cooled to room temperature, and then the filter cake is collected by filtration. After the filter cake is washed 3 times with ultrapure water and methanol respectively, it is dried in a blast dryer at 60 °C for 12 hours to obtain the nitrogen-doped hollow carbon tube loaded with platinum nanoparticles.

[0028] Characterization results of the product obtained in Example 2:

[0029] Figure 2 It is the aberration-corrected transmission electron microscope image of the nitrogen-doped hollow carbon tube loaded with Ru obtained in Example 2. This result shows that nano-metals have been uniformly loaded on the hollow carbon tube. In the high-angle annular dark-field imaging mode, the high-contrast white bright spots are metal sites, and the metal site in Example 1 is nano-Ru. This result indicates that by loading the borane cluster weak reductant on the carbon support to in-situ reduce and prepare the supported nano-Ru, the weak reducibility of the borane cluster can be used to avoid the agglomeration of Ru; when the reductant is introduced onto the carbon support, the hard support effect of the carbon support can also prevent the formed nano-Ru from aggregating on a large scale.

[0030]

Example 3

[0031] Weigh 313.0 mg (0.5 mmol) of TBA2(B12H12) (TBA is tetrabutylammonium cation, and B12H12 is dodecahydrododecaborate cluster anion) and dissolve it in 50 mL of methanol. Then add the nitrogen-doped hollow carbon tube support dissolved in 50 mL of methanol. Subsequently, 500 mL of ultrapure water is added dropwise to the above mixture under stirring conditions. The solid is separated by suction filtration, and the filter cake is washed 3 times with ultrapure water to obtain the nitrogen-doped hollow carbon tube coated with borane cluster reducing agent on its surface. The nitrogen-doped hollow carbon tube coated with borane cluster on its surface is dispersed again in 200 mL of ultrapure water (the container is a 500 mL round-bottom flask), and the round-bottom flask is transferred to an oil bath at 120 °C. Under reflux conditions, 20 mL of potassium hexachloroplatinate solution (the amount of substance is 0.05 mol) and 20 mL of ruthenium trichloride solution (the amount of substance is 0.05 mol) are injected into the mixed dispersion; after reacting for 2 hours, the reaction solution is cooled to room temperature, and then the filter cake is collected by filtration. After the filter cake is washed 3 times with ultrapure water and methanol respectively, it is dried in a blast dryer at 60 °C for 12 hours to obtain the nitrogen-doped hollow carbon tube loaded with platinum nanoparticles.

[0032] Characterization results of the product obtained in Example 3:

[0033] Figure 3 It is the aberration-corrected transmission electron microscope image of the nitrogen-doped hollow carbon tube loaded with Pt and Ru simultaneously obtained in Example 3. The result shows that the hollow carbon tube has been uniformly loaded with nano-metals. In the high-angle annular dark-field imaging mode, the high-contrast white bright spots are metal sites, and the metal sites in Example 3 are nano-PtRu alloy. This result indicates that loading the borane cluster weak reducing agent on the carbon support can also simultaneously prepare multi-metal alloys, and the weak reducibility of the borane cluster can be used to avoid the agglomeration of nano-alloys.

[0034]

Example 4

[0035] Weigh 313.0 mg (0.5 mmol) of TBA2(B12H12) (TBA is tetrabutylammonium cation, and B12H12 is dodecahydrododecaborate cluster anion), dissolve it in 50 mL of methanol, and then add solid mesoporous carbon spheres dissolved in 50 mL of methanol. Subsequently, 500 mL of ultrapure water is added dropwise to the above mixture under stirring conditions. The solid is separated by suction filtration, and the filter cake is washed 3 times with ultrapure water to obtain solid mesoporous carbon spheres embedded with borane cluster reducing agent. The solid mesoporous carbon spheres containing borane clusters are redispersed in 200 mL of ultrapure water (the container is a 500 mL round-bottom flask), and the round-bottom flask is transferred to an oil bath at 120 °C. Under reflux conditions, 20 mL of potassium hexachloroplatinate solution (the amount of substance is 0.05 mol) and 20 mL of ruthenium trichloride solution (the amount of substance is 0.05 mol) are injected into the mixed dispersion; after reacting for 2 hours, the reaction solution is cooled to room temperature, and then the filter cake is collected by filtration. After the filter cake is washed 3 times with ultrapure water and methanol respectively, it is dried in a blast dryer at 60 °C for 12 hours to obtain solid mesoporous carbon spheres loaded with platinum nanoparticles.

[0036] Characterization results of the product obtained in Example 4:

[0037] Figure 4 Powder X-ray diffraction signal of the mesoporous carbon spheres (MCSs) loaded with Pt obtained in Example 4. The signal shows the (111), (200), (220), and (311) crystal planes of Pt, indicating that Pt has been successfully loaded onto the mesoporous carbon spheres.

Claims

1. A method for directly introducing a reducing agent borane cluster into a carbon carrier to prepare nano noble metals, comprising the following steps: A. Introduce the borane cluster weak reducing agent onto the carbon carrier: Dissolve the borane cluster with an organic cation in an organic solvent solution, then add the carbon carrier dispersed well with the organic solvent, and then continuously stir and add the poor solvent water. The purpose is to precipitate the borane cluster from the surface of the carbon carrier and in-situ load it on the carbon carrier. Collect the solid by filtration and dry it to achieve introducing the borane cluster weak reducing agent onto the carbon carrier; B. Reduce metal ions on the carbon carrier containing borane clusters on its surface to prepare nano metals: Redisperse the carbon carrier loaded with borane clusters obtained in step A in water, add an aqueous solution of noble metal salt under reflux at 120 °C, and continuously stir to convert the noble metal ions into nano metals on the carbon carrier. Filter and separate the solid and dry the solid to achieve reducing metal ions on the carbon carrier to prepare nano metals.

2. The preparation scheme according to claim 1, characterized in that, The borane clusters are dodecahydrododecaborate anions, decahydrodecaborate anions, hexahydrohexaborate anions.

3. The preparation scheme according to claim 1, wherein, The cations of the borane clusters are tetrabutylammonium cations, protonated triethylammonium cations, tetraethylammonium cations.

4. The preparation scheme according to claim 1, characterized in that, The organic solvents are methanol, ethanol, acetonitrile, ethyl acetate, dichloromethane, chloroform.

5. The preparation scheme according to claim 1, characterized in that, The noble metal salts can be chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, ruthenium trichloride, sodium chloropalladate, tetrachloroauric acid, iridium trichloride.

6. According to the preparation schemes described in claims 1-5, hollow carbon tube materials loaded with nano noble metal platinum, hollow carbon tube materials loaded with nano noble metal ruthenium, hollow carbon tube materials loaded with nano noble metal platinum-ruthenium, and mesoporous carbon sphere materials loaded with nano noble metal platinum are constructed.

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